(a) Field of the Invention
The present invention relates to sailing boats, and more particularly to an improved keel design for a sailing boat, and also to a method of operating a sail boat.
(b) Brief Description of the Prior Art
A type of conventional sailing boat which has been in existence for many centuries is one which comprises a hull, a sail assembly, and a keel structure. While the function of the keel structure will be discussed in more detail later, it can be stated generally that the main function of the keel is to act as a vertically oriented hydrofoil which resists lateral movement of the boat so that the boat can travel on an angled course in an upwind direction. Also, quite often the keel is weighted so as to add ballast and lower the center of gravity of the boat to enhance the stability of the boat. While there have been many refinements in such sailing boats, this basic design of sailing boats has for many centuries been the one most commonly used.
Also known in the prior art are other applications of hydrofoils in boats. One of the best known applications of hydrofoils is to lift the hull of the boat out of the water so that the hull is being supported entirely by the lifting force provided by the hydrofoils traveling through the water. One of the main advantages of such a design is the relatively high speed with which the boat can travel over the water.
There have been other proposed applications of hydrofoils in boats, mainly to provide adequate stability. One such application is shown in U.S. Pat. No. 1,499,900, Zukucker, where a plurality of fins are provided on two sides of a power boat. These fins may be adjusted both upwardly and downwardly to improve the stability of the boat. In two other patents, U.S. Pat. Nos. 3,377,975, Field, and 3,842,777, Larsh, laterally extending fins are provided on opposite sides of a ship to alleviate any roll condition of the ship.
There have also been various attempts in the prior art to stabilize sailing vessels by the use of hydrofoils. For example, in U.S. Pat. No. 1,356,300, McIntire, there are a pair of "stabilizing planes" mounted at the outer end of outrigger arms. Each stabilizing plane is slanted at a downward and inward inclination. When the vessel is traveling at an angle to the wind so that the wind is exerting a lateral force on the boat to cause it to yaw, the two stabilizing planes not only provide a resisting lateral force, but also exert moments which tend to keep the vessel in an upright position.
A quite similar arrangement is shown in U.S. Pat. No. 3,949,695, Pless, where there are a pair of hydrofoil members mounted at the outer ends of outrigger arms on opposite sides of the hull. These hydrofoils function to stabilize the vessel in generally the same manner as the apparatus shown in the McIntire patent. In addition, the hydrofoils are rotatedly mounted in such a manner that when the vessel is yawing, the two hydrofoils automatically change their angle of attack to augment the lift and thus contribute to the stability of the craft to a greater extent.
U.S. Pat. No. 4,058,076, Danahy, shows a hydrofoil device which functions generally in the same manner as those in the McIntire patent and the Pless patent noted above. However, in the Danahy patent, the hydrofoil members extend from opposite sides of the hull downwardly to a central location beneath the hull.
There have been other attempts in the prior art to utilize hydrofoils in combination with sailing vessels in such a manner as to lift the hull of the vessel totally out of the water. One such device is shown in U.S. Pat. No. 3,373,710, Steinberg, where there is a hydrfoil positioned beneath the boat, this hydrofoil being provided with a set of "ailerons". These ailerons are intended to function in somewhat the same manner as ailerons on a conventional aircraft to maintain the sailboat in an upright position. A somewhat more complex arrangement is shown in U.S. Pat. No. 3,800,724, Tracy. This shows a "winged sailing craft" which has a vertical airfoil to provide a force for forward travel, and a horizontal airfoil to provide stability. In addition, there are provided upper and lower hydrofoils. The upper hydrofoil serves to lift the vessel out of the water at lower speeds, and the lower hydrofoil is arranged to travel through the water to provide either positive or negative lifting forces as required.
U.S. Pat. No. 3,505,968, Gorman, shows a hydrofoil which is mounted below a hull of a sailboat in a manner to function generally as a conventional keel. The hydrodynamic shape of the hydrofoil is not symmetrical so as to improve its "lift" characteristics, and it's mounted for rotation about a horizontal longitudinal axis so that its lifting force can be exerted laterally to one side or the other. As a third alternate arrangement, the hydrofoil is turned so as to provide an upward lifting force when the boat is running with the wind.
Finally, U.S. Pat. No. 3,237,582, Sturgeon et al, illustrates a particular form of a disk hydrofoil which is contended to overcome some of the problems of "skin friction".